where the FL function is the Focal Loss [1]} with its own \(\gamma \)  value equal to 1.5 and \(t_i\)  represents the binary target label.
For the \(i^{th}\)  bounding box, the branch output \(q_{i}^{IoU} \in [0, 1]\)  is a single value which predicts if it is a high- or low-quality bounding box. The target \(t_i\)  and its IoU are defined as follows:
\(\begin{split}IoU_i &= \max {\textrm {IoU}\left(b_i^t,g\right)}\:\:\:\:\:\forall b_{i} \in \mathbf {B} | IoU\left(b_i,g\right) \geqslant u \\t_i &={\left\lbrace \begin{array}{ll}1 & IoU_i > \mu \\0 & \textrm {otherwise} \\\end{array}\right.}\end{split}\) 
